Problem: $ { \left[\begin{array}{rr}{1} & {4} \\ {0} & {4} \\ {-1} & {2}\end{array}\right]+\left[\begin{array}{rr}{-1} & {0} \\ {1} & {-1} \\ {2} & {1}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{1}+{-1} & {4}+{0} \\ {0}+{1} & {4}+{-1} \\ {-1}+{2} & {2}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{0} & {4} \\ {1} & {3} \\ {1} & {3}\end{array}\right]}$